Color toner printers provide full color images by building up and sequentially transferring individual color separation toner images in registration onto a receiver and fusing the toner and receiver. Specific color outcomes are achieved in such printers because controlled ratios of differently colored toners are applied in combination to create the appearance of a desired color at specific locations on a receiver. Similarly, as is described in U.S. Patent Publication Number: US20090286177A1, entitled “Adjustable Gloss Document Printing” different toners such as high viscosity toners can be used in combination with lower viscosity toners to allow a user to obtain a desired gloss level at specific locations by controlling the ratio of two different types of toners at the locations. It will be appreciated that many other desirable printing outcomes can be achieved using ratio controlled combinations of toners.
In tandem type toner printers, separate toner images are generated in individual toner printing modules and the different toners to be applied at a specific location on a printer are combined when the separate toner images are transferred onto a common surface. Accordingly, variations in the way in which the individual toner printing modules generate toner images and variations in the registration of the individual toner images during transfer can create unintended combinations of toner.
It is a continuing objective in the toner printing arts to provide printing systems and methods that can reliably and controllably deliver precise combinations of two or more toners on a receiver. This is driven among other things by requirements for increased image quality, security printing features such as authentication markings, and functional printing objectives. Accordingly, there is an ongoing desire in the printing industry to provide increasing smaller areas in which combinations of toners can reliably be formed in controlled patterns.
In toner printing, toner is developed on a surface having a charge pattern. In analog systems, a charge pattern is formed on the surface in response to an optical image. This form of image patterning can form any of a vast range of different image intensities and depending on the way in which the surface reacts to the image the charge pattern can include an equally wide range of different charge patterns.
In digital printing systems, a digitally controlled writer generates a charge pattern. Such writers provide a fixed number of individually addressable areas which represent the smallest portions of the surface on which different charge levels can be defined by the writer. The writer also has a fixed number of writing levels that it can generate to form the charge pattern. For a given printing system, the size of the individually addressable areas is fixed as is the number of different charge levels that can be assigned to an individually addressable area.
What is needed in the art is a new approach to toner printing that enables the formation of controlled patterns of more than one toner at sizes that are smaller than the presently available addressable areas of such toner printers.